diff --git a/Tests/LibWeb/Text/expected/HTML/Window-postMessage.txt b/Tests/LibWeb/Text/expected/HTML/Window-postMessage.txt
index d1b09cd76c..7db9d9d37a 100644
--- a/Tests/LibWeb/Text/expected/HTML/Window-postMessage.txt
+++ b/Tests/LibWeb/Text/expected/HTML/Window-postMessage.txt
@@ -32,6 +32,9 @@ Message 1 data: undefined
 Message 1 origin: file://
 Message 1 lastEventId: 
 Message 1 source: [object Window]
+Message 1 ports: 
+Message 1 ports === ports: true
+Message 1 Object.isFrozen(ports): true
 Message 1 source === window: true
 Message 1 source === iframe.contentWindow: false
 Message 1 source === blobIframe.contentWindow: false
@@ -39,6 +42,9 @@ Message 2 data: null
 Message 2 origin: file://
 Message 2 lastEventId: 
 Message 2 source: [object Window]
+Message 2 ports: 
+Message 2 ports === ports: true
+Message 2 Object.isFrozen(ports): true
 Message 2 source === window: true
 Message 2 source === iframe.contentWindow: false
 Message 2 source === blobIframe.contentWindow: false
@@ -46,6 +52,9 @@ Message 3 data: true
 Message 3 origin: file://
 Message 3 lastEventId: 
 Message 3 source: [object Window]
+Message 3 ports: 
+Message 3 ports === ports: true
+Message 3 Object.isFrozen(ports): true
 Message 3 source === window: true
 Message 3 source === iframe.contentWindow: false
 Message 3 source === blobIframe.contentWindow: false
@@ -53,6 +62,9 @@ Message 4 data: false
 Message 4 origin: file://
 Message 4 lastEventId: 
 Message 4 source: [object Window]
+Message 4 ports: 
+Message 4 ports === ports: true
+Message 4 Object.isFrozen(ports): true
 Message 4 source === window: true
 Message 4 source === iframe.contentWindow: false
 Message 4 source === blobIframe.contentWindow: false
@@ -60,6 +72,9 @@ Message 5 data: 123
 Message 5 origin: file://
 Message 5 lastEventId: 
 Message 5 source: [object Window]
+Message 5 ports: 
+Message 5 ports === ports: true
+Message 5 Object.isFrozen(ports): true
 Message 5 source === window: true
 Message 5 source === iframe.contentWindow: false
 Message 5 source === blobIframe.contentWindow: false
@@ -67,6 +82,9 @@ Message 6 data: 123.456
 Message 6 origin: file://
 Message 6 lastEventId: 
 Message 6 source: [object Window]
+Message 6 ports: 
+Message 6 ports === ports: true
+Message 6 Object.isFrozen(ports): true
 Message 6 source === window: true
 Message 6 source === iframe.contentWindow: false
 Message 6 source === blobIframe.contentWindow: false
@@ -74,6 +92,9 @@ Message 7 data: 9007199254740991
 Message 7 origin: file://
 Message 7 lastEventId: 
 Message 7 source: [object Window]
+Message 7 ports: 
+Message 7 ports === ports: true
+Message 7 Object.isFrozen(ports): true
 Message 7 source === window: true
 Message 7 source === iframe.contentWindow: false
 Message 7 source === blobIframe.contentWindow: false
@@ -81,20 +102,39 @@ Message 8 data: This is a string
 Message 8 origin: file://
 Message 8 lastEventId: 
 Message 8 source: [object Window]
+Message 8 ports: 
+Message 8 ports === ports: true
+Message 8 Object.isFrozen(ports): true
 Message 8 source === window: true
 Message 8 source === iframe.contentWindow: false
 Message 8 source === blobIframe.contentWindow: false
-Message 9 data: I am from another ~planet~ iframe
+Message 9 data: [object Object]
 Message 9 origin: file://
 Message 9 lastEventId: 
 Message 9 source: [object Window]
-Message 9 source === window: false
-Message 9 source === iframe.contentWindow: true
+Message 9 ports: [object MessagePort]
+Message 9 ports === ports: true
+Message 9 Object.isFrozen(ports): true
+Message 9 source === window: true
+Message 9 source === iframe.contentWindow: false
 Message 9 source === blobIframe.contentWindow: false
-Message 10 data: All done :^)
+Message 10 data: I am from another ~planet~ iframe
 Message 10 origin: file://
 Message 10 lastEventId: 
 Message 10 source: [object Window]
+Message 10 ports: 
+Message 10 ports === ports: true
+Message 10 Object.isFrozen(ports): true
 Message 10 source === window: false
-Message 10 source === iframe.contentWindow: false
-Message 10 source === blobIframe.contentWindow: true
\ No newline at end of file
+Message 10 source === iframe.contentWindow: true
+Message 10 source === blobIframe.contentWindow: false
+Message 11 data: All done :^)
+Message 11 origin: file://
+Message 11 lastEventId: 
+Message 11 source: [object Window]
+Message 11 ports: 
+Message 11 ports === ports: true
+Message 11 Object.isFrozen(ports): true
+Message 11 source === window: false
+Message 11 source === iframe.contentWindow: false
+Message 11 source === blobIframe.contentWindow: true
diff --git a/Tests/LibWeb/Text/input/HTML/Window-postMessage.html b/Tests/LibWeb/Text/input/HTML/Window-postMessage.html
index fa2ee130f7..ec8f9608d6 100644
--- a/Tests/LibWeb/Text/input/HTML/Window-postMessage.html
+++ b/Tests/LibWeb/Text/input/HTML/Window-postMessage.html
@@ -3,7 +3,7 @@
 <body>
     <script>
         window.addEventListener('message', (event) => {
-            window.parent.postMessage(event.data, '*');
+            window.parent.postMessage(event.data, '*', event.ports);
         });
     </script>
 <body>
@@ -30,6 +30,9 @@
             println(`Message ${messageCount} origin: ${messageEvent.origin}`);
             println(`Message ${messageCount} lastEventId: ${messageEvent.lastEventId}`);
             println(`Message ${messageCount} source: ${messageEvent.source}`);
+            println(`Message ${messageCount} ports: ${messageEvent.ports}`);
+            println(`Message ${messageCount} ports === ports: ${messageEvent.ports === messageEvent.ports}`);
+            println(`Message ${messageCount} Object.isFrozen(ports): ${Object.isFrozen(messageEvent.ports)}`);
             println(`Message ${messageCount} source === window: ${messageEvent.source === window}`);
             println(`Message ${messageCount} source === iframe.contentWindow: ${messageEvent.source === iframe.contentWindow}`);
             println(`Message ${messageCount} source === blobIframe.contentWindow: ${messageEvent.source === blobIframe.contentWindow}`);
@@ -55,6 +58,8 @@
         window.postMessage("This is a string", "/");
         window.postMessage("I shouldn't appear, I'm not same origin!", "https://serenityos.org");
         iframe.contentWindow.postMessage("I am from another ~planet~ iframe", "*");
+        let channel = new MessageChannel();
+        window.postMessage({foo: [channel.port1]}, "*", [channel.port1]);
         blobIframe.contentWindow.postMessage("All done :^)", iframeSrcdocBlobUrl);
 
         try {
diff --git a/Userland/Libraries/LibWeb/HTML/Window.cpp b/Userland/Libraries/LibWeb/HTML/Window.cpp
index e2327d3f6d..66310e4800 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Window.cpp
@@ -10,6 +10,7 @@
 #include <AK/DeprecatedString.h>
 #include <AK/GenericLexer.h>
 #include <AK/Utf8View.h>
+#include <LibIPC/File.h>
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Accessor.h>
 #include <LibJS/Runtime/Completion.h>
@@ -1062,11 +1063,10 @@ WebIDL::ExceptionOr<void> Window::window_post_message_steps(JS::Value message, W
     }
 
     // 6. Let transfer be options["transfer"].
-    // FIXME: This is currently unused.
+    auto& transfer = options.transfer;
 
     // 7. Let serializeWithTransferResult be StructuredSerializeWithTransfer(message, transfer). Rethrow any exceptions.
-    // FIXME: Use StructuredSerializeWithTransfer instead of StructuredSerialize
-    auto serialize_with_transfer_result = TRY(structured_serialize(target_realm.vm(), message));
+    auto serialize_with_transfer_result = TRY(structured_serialize_with_transfer(target_realm.vm(), message, transfer));
 
     // 8. Queue a global task on the posted message task source given targetWindow to run the following steps:
     queue_global_task(Task::Source::PostedMessage, *this, [this, serialize_with_transfer_result = move(serialize_with_transfer_result), target_origin = move(target_origin), &incumbent_settings, &target_realm]() {
@@ -1086,11 +1086,9 @@ WebIDL::ExceptionOr<void> Window::window_post_message_steps(JS::Value message, W
         auto& source = verify_cast<WindowProxy>(incumbent_settings.realm().global_environment().global_this_value());
 
         // 4. Let deserializeRecord be StructuredDeserializeWithTransfer(serializeWithTransferResult, targetRealm).
-        // FIXME: Use StructuredDeserializeWithTransfer instead of StructuredDeserialize
-        // FIXME: Don't use a temporary execution context here.
         auto& settings_object = Bindings::host_defined_environment_settings_object(target_realm);
         auto temporary_execution_context = TemporaryExecutionContext { settings_object };
-        auto deserialize_record_or_error = structured_deserialize(vm(), serialize_with_transfer_result, target_realm, Optional<HTML::DeserializationMemory> {});
+        auto deserialize_record_or_error = structured_deserialize_with_transfer(vm(), serialize_with_transfer_result);
 
         // If this throws an exception, catch it, fire an event named messageerror at targetWindow, using MessageEvent,
         // with the origin attribute initialized to origin and the source attribute initialized to source, and then return.
@@ -1105,20 +1103,27 @@ WebIDL::ExceptionOr<void> Window::window_post_message_steps(JS::Value message, W
         }
 
         // 5. Let messageClone be deserializeRecord.[[Deserialized]].
-        // FIXME: Get this from deserializeRecord.[[Deserialized]] once it uses StructuredDeserializeWithTransfer instead of StructuredDeserialize.
-        auto message_clone = deserialize_record_or_error.release_value();
+        auto deserialize_record = deserialize_record_or_error.release_value();
+        auto message_clone = deserialize_record.deserialized;
 
-        // FIXME: 6. Let newPorts be a new frozen array consisting of all MessagePort objects in deserializeRecord.[[TransferredValues]],
-        //           if any, maintaining their relative order.
+        // 6. Let newPorts be a new frozen array consisting of all MessagePort objects in deserializeRecord.[[TransferredValues]],
+        //    if any, maintaining their relative order.
+        // FIXME: Use a FrozenArray
+        Vector<JS::Handle<JS::Object>> new_ports;
+        for (auto const& object : deserialize_record.transferred_values) {
+            if (is<HTML::MessagePort>(*object)) {
+                new_ports.append(object);
+            }
+        }
 
         // 7. Fire an event named message at targetWindow, using MessageEvent, with the origin attribute initialized to origin,
         //    the source attribute initialized to source, the data attribute initialized to messageClone, and the ports attribute
         //    initialized to newPorts.
-        // FIXME: Set the ports attribute to newPorts.
         MessageEventInit message_event_init {};
         message_event_init.origin = MUST(String::from_deprecated_string(origin));
         message_event_init.source = JS::make_handle(source);
         message_event_init.data = message_clone;
+        message_event_init.ports = move(new_ports);
 
         auto message_event = MessageEvent::create(target_realm, EventNames::message, message_event_init);
         dispatch_event(message_event);